Color inconstancy is the undesirable change in color of an object caused by a change in illumination. Conversely, color constancy is the tendency of the color of an object to remain constant when the level and color of the illumination are changed. Color inconstancy is typically unavoidable, which means that colors tend to be perceived differently under different illuminants. Color inconstancy is a very important factor to evaluate for the image quality of prints since prints tend to be viewed under a wide variety of differing lighting sources and conditions. For example, color inconstancy occurs frequently when profiles are created for standardized daylight but are viewed under narrow-band fluorescent illumination. This can be an acute problem depending on the spectral properties of the inks used in the print process and the method of building the color look-up table (CLUT). FIG. 1 shows some printing samples with relatively large color inconstancy between standard daylight (D50) and fluorescent (F11) light sources. In FIG. 1, the tail of the illustrated arrows represents the tristimulus values of prints under fluorescent lighting (F11) and the head of the arrows represents the tristimulus values under standard daylight (D50).
For a specific print device, it's color inconstancy range is determined by its ink set and the substrate employed. In order to explore the color inconstancy property for a given print device, a virtual printer model needs to be developed which is based upon the spectral reflectances of the inks and substrates used by that printer. Though the virtual printer model cannot provide a highly accurate prediction for a specific spot color, it can be used to evaluate some basic properties of printers, such as color inconstancy. No common theory exists to explain the various mechanism of color constancy on the human visual system. It is important that color materials, especially those in color print, exhibit color constancy. A seasoned color expert (human) may be able to visually determine which spot colors are best to use on a given marking device from a color constancy perspective. However, the average user/customer of document reproduction devices is not likely to have the experience and visual acuity to select colors best viewed under different lighting sources. Having precise metrics, from a color constancy perspective, for a given spot color at the start of a print/copy job greatly benefits system operators in their print/copy job environments. Such metrics are further needed by designer of color documents, color brochures, logos, and the like, who need to have metrics useful for selecting colors which will likely look the same under various illuminants once rendered.
Accordingly, what is needed in this art are increasingly sophisticated systems and methods for generating a color inconstancy guide for use in spot color print applications in a print/copy job environment.